The present invention relates to a new and improved strap dispenser, particularly a dispenser in which strap is supplied in coils of substantial weight, wherein the weight of the coil is used to initiate and terminate dispensing with minimal shock loads to the dispenser and without strap overrun.
It has been found that the mass and inertia of strap coils, particularly when they are fresh and have relatively great weight, produce a large shock load on the strap feeding mechanism of the strapping machine when dispensing is terminated. This is due to the stopping mechanisms of the prior art, which must absorb the large rotational energy of the rotating coil to terminate its rotation.
Another problem associated with prior art strap dispensers is that rotational inertia will cause the strap from these coils to overrun when the feed to the strapping machine has been terminated, unless the rotation is very quickly terminated. This overrunning can leave a substantial length of strap lying loose between the coil and the feed mechanism of the strapping machine, which can cause tangling and which increases the opportunity for snagging of the strap when feed is again commenced.
Various apparatus has been suggested in the past for dispensing strap in an effort to meet the above mentioned problems, and representative prior art patents are discussed herebelow. For various reasons these apparatus are not particularly suitable for large mass coils.
Forbes U.S. Pat. No. 1,144,831, discloses a tubular feeding slide to prevent the coil from opening during dispensing, but does not disclose any means for solving the overrunning and stopping problems. In Porter U.S. Pat. No. 2,155,771, circumferential ring springs are disclosed to provide a continuous braking action to prevent overrunning of the strap. However, such continuous braking inhibits the dispensing of strap and produces excessive wear on the brake elements. These disadvantages were recognized in Green U.S. Pat. No. 2,506,554, which discloses a rim riding rotating feeder brake which reduced, if not substantially eliminated, braking during the dispensing operation. However, the Green brake has little applicability to large mass coil dispensers which generate high rotational energy. Coils were eventually power fed as in Leslie U.S. Pat. No. 2,779,410, in which the strapping was drawn from the center of the coil, and back pressure on the feed was used to prevent overrunning.